1. Field of the Invention
The present invention relates to a drive apparatus for a zoom lens barrel.
2. Description of the Related Art
A zoom lens includes at least two movable lens groups which are moved in predetermined directions upon zooming. In many zoom lenses, one of the two lens groups functions as a focusing lens group. In a conventional or classical drive mechanism which has been used particularly for a single lens reflex camera in which no focal shift during zooming is accepted, the movable zoom lens groups are moved along tracks defined by cam grooves formed on a cam ring so as not to cause the focal shift. The position of the focusing lens group, one of the two movable lens groups is controlled in accordance with the object distance upon focusing.
In another type of known drive mechanism for compact cameras or digital cameras in which it is necessary to correctly focus on an object at the time of shutter releasing, the movable zoom lens groups are moved upon zooming while permitting the focal shift, and thereafter the movable lens groups are moved to a focal position in accordance with set focal length data and set object distance data upon the shutter releasing.
In the conventional drive apparatuses, separate drive motors for the zooming operation and the focusing operation or for the two movable lens groups must be used. Moreover, it is necessary to provide a position detecting mechanism of the movable lens groups.